This invention relates to apparatus for automatic, precise placement of objects, e.g., placing semiconductor wafers in holders or boats.
It is desirable to rapidly transfer semiconductor wafers from plastic storage boats to quartz boats (in which they are introduced into a diffusion furnace), and vice versa, without introducing contamination onto the surfaces of the wafers. Such contamination often results during wafer placement in the quartz boats, from the wafers scraping against the slots into which they are placed. These slots are only slightly wider than the wafers themselves, and thus it has been difficult to achieve sufficiently precise placement as to avoid such scraping altogether. Contamination can also arise from scraping and sliding of parts within the apparatus being used to accomplish the transfer.
It is also desirable to be able to move arms and receptacles and the like (e.g., elements of a robot) to and from precise locations with good repeatabilty (i.e., such that they arrive back at the same location after being moved away temporarily). In apparatus for transferring semiconductor wafers, the wafer boats and the wafer transfer arm must both generally be moved about with precision.